Re: [PATCH 3/3 v2] perf tool: give user better message if precise isnot supported

From: Ingo Molnar
Date: Fri Sep 14 2012 - 01:43:41 EST

* David Ahern <dsahern@xxxxxxxxx> wrote:

> Platforms (e.g., VM's) without support for precise mode get a confusing
> error message. e.g.,
> $ perf record -e cycles:p -a -- sleep 1
> Error: sys_perf_event_open() syscall returned with 95 (Operation not
> supported). /bin/dmesg may provide additional information.
> No hardware sampling interrupt available. No APIC? If so then you can
> boot the kernel with the "lapic" boot parameter to force-enable it.
> sleep: Terminated
> which is not clear that precise mode might be the root problem. With this
> patch:
> $ perf record -e cycles:p -fo /tmp/ -- sleep 1
> Error:
> 'precise' request may not be supported. Try removing 'p' modifier
> sleep: Terminated
> v2: softened message to 'may not be' supported per Robert's suggestion

Well, either it's supported on this machine or it's not - why
does the text have to be so unsure about it?

We use computers to increase determinism, not to insert extra
uncertainty! ;-)


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